In recent years, solar power generation technologies in which solar energy, which is one of renewable energies, is used without using fossil fuels, as a means for solving the problem of global warming, have gained attention. Among the solar power generation technologies, a pigment-sensitized solar cell attracts lots of attention as one of inexpensive, high-performance roof-top type solar cells that are responsible for the next generation, since it generates electricity by a similar mechanism to that of light-induced electron transfer conducted by a chlorophyll pigment.
A general constitution of such pigment-sensitized solar cell is such that a substrate, a first electrode, a semiconductor layer on which a sensitizing pigment is carried (a photoelectric conversion layer), a hole transport layer, and a second electrode are stacked in this order. For example, the technology for a pigment-sensitized solar cell includes Patent Literature 1. This Patent Literature 1 discloses a photoelectric conversion element including a second electrode in which platinum is supported on a transparent conductive glass plate coated with fluorine-doped tin oxide as a counter electrode for electrolysis, and an electrolytically-polymerized aniline film is formed on the counter electrode by leaving a predetermined size of a platinum part on the central part of the electrode surface, masking the other parts by a imide-based resin tape, and immersing the counter electrode in an acidic aqueous solution including aniline and hydrogen fluoroborate, and energizing the counter electrode at a predetermined current density, and a production method therefor, and a photoelectric conversion element formed by immersing this electrolytically-polymerized film of aniline in a liquid electrolyte, and a production method therefor.
Furthermore, in the case when an electrolyte is used as in the above-mentioned Patent Literature 1, the leaking or depletion of the electrolyte may occur, and thus there are technologies using a solid electrolyte as a hole transport layer. In Patent Literature 2, which is one of the technologies, discloses that a mesoporous titanium dioxide porous layer, which is a photoelectric conversion layer, is immersed in an acetonitrile solution in which pyrrole and LiClO4 are dissolved, the retention voltage is set to 250 mV, platinum is used as a counter electrode, Ag/Ag+ is used as a reference electrode, light is irradiated, and the voltage is retained until the polymerization electrical charge amount becomes a predetermined value, and also discloses a photoelectric conversion element in which a polypyrrole layer as a hole transport layer is formed onto the layer surface of the above-mentioned photoelectric conversion layer and a production method therefor.